This invention relates to an air conditioning system for use in automotive vehicles, and more particularly to an air conditioning system of this kind which is adapted to prevent seizure of component parts of its compressor or like failure attributable to a shortage of refrigerant.
Conventionally, an air conditioning system for automotive vehicles has been proposed by Japanese Provisional Utility Model Publication (Kokai) No. 51-1943, which comprises a compressor driven by the automotive engine to compress the refrigerant, an electromagnetic clutch interposed between the driving shaft of the compressor and the output shaft of the engine, a condenser for cooling the refrigerant compressed by the compressor to liquefy same, an expansion valve for controlling the flow rate of the liquefied refrigerant to proper values corresponding to thermal load on the system, an evaporator for evaporating the liquefied refrigerant and thus cooling the air to be blown into the passenger compartment through heat exchange thereof with the refrigerant, a temperature sensor and a pressure sensor for detecting, respectively, the temperature and pressure of the refrigerant at an outlet of the evaporator, and a valve control means for controlling the opening of the expansion valve in response to output signals from the temperature sensor and the pressure sensor.
According to this conventional air conditioning system, the pressure and temperature of the refrigerant at the outlet of the evaporator are detected, and when the overheating degree determined from these detected values exceeds a certain value, the electromagnetic clutch is disengaged so as to prevent seizure of sliding parts of the compressor, while an alarm device is actuated. In this conventional system, the detected temperature of the refrigerant at the outlet of the evaporator is mechanically converted into corresponding pressure to be applied to one side surface of a diaphragm while the other side surface thereof is subjected to the detected pressure of the refrigerant at the outlet, and when the deflection of the diaphragm, corresponding to the difference between the two pressures, reaches a predetermined value, the electromagnetic clutch is disengaged, and an alarm device is actuated. However, this conventional system requires the provision of exclusive parts such as the diaphragm and oil passage conduits, thus being disadvantageous costwise.